1. Field of the Invention
The present invention relates to 5-oxo-2-pyrazolines and to a process for producing same. More particularly, it relates to 1,3,4 -trisubstituted-5-oxopyrazolines substituted with a piperidino group in the 4-position and a process for producing same.
In particular, a characteristic aspect of the present invention is to produce 5-oxo-2-pyrazolines by reducing 5-oxo-2-pyrazoline 4-pyridinium salt derivatives.
2. Description of the Prior Art
It is well known that 1,3-di-substituted-5-oxo-2-pyrazolines are important compounds as magenta couplers for color photographic light-sensitive materials utilizing the color subtractive process and are useful as intermediates for many medicines and dyes. For example, when an exposed conventional color photographic light-sensitive material having a silver halide emulsion containing a 1,3-di-substituted-5-oxo-2-pyrazoline is subjected to color development-processing, the color coupler oxidatively couples with the oxidized p-phenylenediamine color developing agent to form a corresponding azomethine dye.
It is well known that four equivalents of silver halide are theoretically necessary as an oxidizing agent in order to form one molecule of an azomethine dye through the color coupling reaction of such a 1,3-di-substituted-5-oxo-2-pyrazoline coupler. In contrast, 1,3,4-trisubstituted-5-oxo-2-pyrazolines containing in the 4-position a substituent which can be eliminated easily after the coupling reaction with an oxidized color developing agent theoretically require only two equivalents of silver halide to form the dye.
For this reason, 5-oxo-2-pyrazolines having an eliminatable substituent in the 4-position are extremely important compounds in the production of color photographic light-sensitive materials.